To determine whether defects in the insulin signal transduction pathway to glucose transport occur in a muscle fiber type-specific manner, post-receptor insulin-signaling events were assessed in oxidative (soleus) and glycolytic (extensor digitorum longus [EDL]) skeletal muscle from Wistar or diabetic GK rats. In soleus muscle from GK rats, maximal insulin-stimulated (120 nmol/l) glucose transport was significantly decreased, compared with that of Wistar rats. In EDL muscle from GK rats, maximal insulin-stimulated glucose transport was normal, while the submaximal response was reduced compared with that of Wistar rats. We next treated diabetic GK rats with phlorizin for 4 weeks to determine whether restoration of glycemia would lead to improved insulin signal transduction. Phlorizin treatment of GK rats resulted in full restoration of insulin-stimulated glucose transport in soleus and EDL muscle. In soleus muscle from GK rats, submaximal and maximal insulin-stimulated insulin receptor substrate (IRS)-1 tyrosine phosphorylation and IRS-1-associated phosphatidylinositol (PI) 3-kinase activity were markedly reduced, compared with that of Wistar rats, but only submaximal insulin-stimulated PI 3-kinase was restored after phlorizin treatment. In EDL muscle, insulin-stimulated IRS-1 tyrosine phosphorylation and IRS-1-associated PI-3 kinase were not altered between GK and Wistar rats. Maximal insulin-stimulated Akt (protein kinase B) kinase activity is decreased in soleus muscle from GK rats and restored upon normalization of glycemia (Krook et al., Diabetes 46:2100-2114, 1997). Here, we show that in EDL muscle from GK rats, maximal insulin-stimulated Akt kinase activity is also impaired and restored to Wistar rat levels after phlorizin treatment. In conclusion, functional defects in IRS-1 and PI 3-kinase in skeletal muscle from diabetic GK rats are fiber-type-specific, with alterations observed in oxidative, but not glycolytic, muscle. Furthermore, regardless of muscle fiber type, downstream steps to PI 3-kinase (i.e., Akt and glucose transport) are sensitive to changes in the level of glycemia.

Rationale: Coronary artery disease (CAD) is the leading cause of death worldwide, but there are currently no methods to stimulate artery growth or regeneration in diseased hearts. Studying how arteries are built during development could illuminate strategies for re-building these vessels during ischemic heart disease. We previously found that Dach1 deletion in mouse embryos resulted in small coronary arteries. However, it was not known whether Dach1 gain-of-function would be sufficient to increase arterial vessels and whether this could benefit injury responses. Objective: We investigated how Dach1 overexpression in endothelial cells affected transcription and artery differentiation, and how it influenced recovery from myocardial infarction (MI). Methods and Results: Dach1 was genetically overexpressed in coronary endothelial cells (ECs) in either developing or adult hearts using ApjCreER. This increased the length and number of arterial end branches expanded arteries during development, in both the heart and retina, by inducing capillary ECs to differentiate and contribute to growing arteries. Single-cell RNA sequencing (scRNAseq) of ECs undergoing Dach1-induced arterial specification indicated that it potentiated normal artery differentiation, rather than functioning as a master regulator of artery cell fate. ScRNAseq also showed that normal arterial differentiation is accompanied by repression of lipid metabolism genes, which were also repressed by Dach1. In adults, Dach1 overexpression did not cause a statistically significant change artery structure prior to injury, but increased the number of perfused arteries in the injury zone post-MI. Conclusions: Our data demonstrate that increasing Dach1 is a novel method for driving artery specification and extending arterial branches, which could be explored as a means of mitigating the effects of CAD.

The response of cerebral arteries to norepinephrine was examined in vivo in six dated preterm fetal (94-121 days gestation), eight term fetal (127-141 days gestation), five newborn (7-14 days), and five adult sheep, anesthetized and equipped with a closed cranial window. Norepinephrine (10(-8)-10(-4) M in cerebrospinal fluid) caused a dose-dependent decrease in pial arteriolar diameter in fetal and newborn lambs; however, preterm fetuses were 7- and 14-fold more sensitive to norepinephrine than term fetuses and newborn lambs, respectively. The effective concentration of norepinephrine inducing a 15% decrease in diameter (EC15) was 4.6 +/- 1.8, 33 +/- 11, and 64 +/- 23 microM, for the respective ages. Adult cerebral arterioles did not contract to norepinephrine. In preterm and term fetuses, the contractile response to norepinephrine was blocked by alpha 1-antagonist, prazosin (3 mg iv), and was enhanced by cocaine (10(-5) M; EC15 = 0.086 +/- 0.04 and 1.84 +/- 1.20 microM, respectively) indicating that alpha 1-adrenoceptors mediate the response and that the decrease in sensitivity is not caused by development of neuronal uptake processes. In seven fetuses (111-141 days; mean 123 days gestation), electrical stimulation of the superior cervical sympathetic ganglion constricted pial arterioles by 21 +/- 5%; this contractile response was also blocked by prazosin. The cerebral arterioles of the fetus in utero possess a functional sympathetic innervation capable of influencing cerebrovascular resistance. There is a loss of responsiveness of cerebral arterioles to norepinephrine during fetal and postnatal development, suggesting that the contribution of neuroadrenergic mechanisms to cerebrovascular regulation may be relatively unique to the immature brain.

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Aims Non-compaction cardiomyopathy is a devastating genetic disease caused by insufficient consolidation of ventricular wall muscle that can result in inadequate cardiac performance. Despite being the third most common cardiomyopathy, the mechanisms underlying the disease, including the cell types involved, are poorly understood. We have previously shown that endothelial cell-specific deletion of the chromatin remodeller gene Ino80 results in defective coronary vessel development that leads to ventricular non-compaction in embryonic mouse hearts. We aimed to identify candidate angiocrines expressed by endocardial and ECs inwildtype and LVNC conditions in Tie2Cre;Ino80fl/fl transgenic embryonic mouse hearts, and test the effect of these candidates on cardiomyocyte proliferation and maturation. Methods and results We used single-cell RNA-sequencing to characterize endothelial and endocardial defects in Ino80-deficient hearts. We observed a pathological endocardial cell population in the non-compacted hearts and identified multiple dysregulated angiocrine factors that dramatically affected cardiomyocyte behaviour. We identified Col15A1 as a coronary vessel-secreted angiocrine factor, downregulated by Ino80-deficiency, that functioned to promote cardiomyocyte proliferation. Furthermore, mutant endocardial and endothelial cells (ECs) up-regulated expression of secreted factors, such as Tgfbi, Igfbp3, Isg15, and Adm, which decreased cardiomyocyte proliferation and increased maturation. Conclusions These findings support a model where coronary ECs normally promote myocardial compaction through secreted factors, but that endocardial and ECs can secrete factors that contribute to non-compaction under pathological conditions.